Hi,

Sometimes you may experience problems in opening your action or action event. In this case, it might have become corrupted somehow. 

You can solve this for either an action or event by changing the word "/show/" in the URL to "/edit/". If it does open normal, please change the corrupt items or delete the action/event.

It's also possible to try and open it in an incognito window. If it works, make sure to clear your cache.